In the direct teaching type robot, an operator directly operates the tip and the wrist of a moving arm of the robot to teach the operation positions thereof to the robot. This teaching method can teach a complicated path to the robot with very short teaching time and is accordingly applied to many robots, specifically most of the so-called painting robots.
However, since large operating force is required to operate the tip and the wrist of the moving arm of the robot, it is difficult to operate them so that the above approach can not be utilized and the operator may suffer physical problems such as lumbago. Accordingly, various methods of reducing the operation force in teaching the robot have been proposed in the past.
In a first method, a balancer is employed to cancel the load moment produced by a load of the moving arm of the robot by the balance force moment produced by the force of the balancer so that the force necessary for the operation is reduced.
In a second method, a clutch is disposed between the moving arm of the robot and a servo-motor and, when the servo-motor is used to operate the moving arm, the clutch is coupled between the moving arm of the robot and the servo-motor while, when the teaching operation is made to the robot, the clutch is disconnected.
FIG. 2 is a block diagram showing an embodiment of the second method.
A moving arm 34 is coupled with a position detector 42 and a signal produced from the position detector 42 is supplied to a robot control circuit 35. The robot control circuit 35 is connected through a servo-amplifier 36 to an ac servo-motor 37 and a signal generated by a pulse generator 38 included in the servo-motor 37 is supplied through the servo-amplifier to the robot control circuit 35. The robot control circuit 35 controls the moving arm 34 of the robot by the feedback control of the position and the speed based on the positional signal and the speed signal.
The servo-amplifier 37 is coupled through a clutch 39 to a reduction gear 40 which is coupled with the moving arm 34. The clutch 39 is coupled with a mode switch 41 which is operated by the operator so that the mode of the robot can be changed from some other mode to a direct teaching mode. When the mode of the robot is changed to the direct teaching mode, the drive mechanism of the clutch 39 is disconnected by the clutch 39 while, in the other mode, the drive mechanism is connected to the clutch 39.
When a command signal for moving the moving arm 34 of the robot is supplied to the servo-amplifier 36 from the robot control circuit 35 in the mode except the direct teaching mode, the servo-amplifier 36 supplies a drive signal to the servo-motor 37 in response to the command signal to drive the motor 37. In this case, since the clutch 39 is connected, the moving arm 34 is operated through the reduction gear 40 by the rotating force of the servo-motor 37.
When the direct teaching operation is performed, the operator operates the mode switch 41 to be the direct teaching mode. At this time, the clutch 39 is disconnected from the servo-motor and the reduction gear so that the coupling between the servo-motor 37 and the reduction gear 40 can be disconnected to remove rotation resistance of the servo-motor 37. In this manner, an electromagnetic clutch or an air clutch is disposed as a part of the power transmission mechanism to remove the rotation resistance of the drive device such as the servo-motor so that the servo-motor is disconnected through the clutch during the teaching operation of the robot to reduce the operating force.
In a third method, as disclosed in Japanese Patent Laid-Open No. 62-94284, a motor current during the operation of the robot is detected to calculate reduction torque for the operating force and the calculated reduction torque is supplied to a motor drive device as the torque command to remove the frictional force due to a back electromotive force.
In a fourth method, as disclosed in Japanese Patent Laid-Open No. 63-162172, the operating force at the beginning of operating the robot is detected by a strain detector and friction compensation torque is supplied to the motor through a strain amplifier and a power amplifier to reduce the operating force.